Liquid crystal display (LCD) is commonly used as a display device because of its capability of displaying images with good quality while using little power. An LCD apparatus includes an LCD panel formed with liquid crystal cells and pixel elements with each associating with a corresponding liquid crystal cell and having a liquid crystal capacitor and a storage capacitor, a thin film transistor (TFT) electrically coupled with the liquid crystal capacitor and the storage capacitor. These pixel elements are substantially arranged in the form of a matrix having a number of pixel rows and a number of pixel columns. Typically, scanning signals are sequentially applied to the number of pixel rows for sequentially turning on the pixel elements row-by-row. When a scanning signal is applied to a pixel row to turn on corresponding TFTs of the pixel elements of a pixel row, source signals (image signals) for the pixel row are simultaneously applied to the number of pixel columns so as to charge the corresponding liquid crystal capacitor and storage capacitor of the pixel row for aligning orientations of the corresponding liquid crystal cells associated with the pixel row to control light transmittance therethrough. By repeating the procedure for all pixel rows, all pixel elements are supplied with corresponding source signals of the image signal, thereby displaying the image signal thereon.
An LCD is a passive display device and usually requires a cold cathode fluorescent lamp to provide backlight to display an image on the LCD screen. A constant brightness backlight is usually provided by a backlight module. Therefore, the contrast ratio of the LCD display is determined by the transmittance of the LCD. Generally, the backlight module is electrically coupled with an input color image signal and the brightness of the backlight module is adjusted according to the input color image signal to be displayed on the LCD screen. The contrast of the LCD display is therefore increased.
For example, as shown in FIG. 8, an optical display system was disclosed by Gergason et al. in U.S. Pat. No. 6,816,141. The display apparatus includes a passive display, a light source, and a video signal input. A method of producing a displayed image was also disclosed by using a passive display illuminated by a light source is characterized in controlling the light source to obtain a displayed image with a desired amount of information, grayscale and/or color characteristics. The light source modulates the light as a function of some type of controlled input, such as a video signal. The transmittance of the LCD cell and the intensity of the backlight are both controlled by the input image signal, resulting an increased contrast of the displayed images.
In recent years, light emitting diode (LED) array modules have emerged as a new backlight source and become increasingly popular because they can provide more vivid and brighter color images. When a red-green-blue (RGB) tri-color LED is used for backlight, the current through these RGB tri-color diodes needs to be adjusted so that the backlight LED module provides a balanced white color backlight. Since the RGB LED intensity may vary with the surrounding temperature from time to time, such variation should be detected and the intensity of the RGB LED should be compensated accordingly so as to keep the color temperature relatively constant.
In an example shown in FIG. 9, a method for adjusting the color temperature in an LCD with backlighting was disclosed by U.S. Pat. No. 6,213,615 to Siitari et al. The LCD is lit by two or more background light lamps (LAMP 1, 2, 3, 4, 5) with different color temperatures, the color temperature range of the backlight lamps (LAMP 1, 2, 3, 4, 5) is extended and better opportunities for adjusting the color temperature by changing the pass rate of the light are provided. In a more advanced solution, backlight lamps (LAMP 1, 2, 3, 4, 5) with different color temperatures are switched on switch SI separately for setting the color temperature of the display, and the brightness of the backlight lamps with different color temperatures can be adjusted separately for setting the color temperature.
However, such backlight devices consume large amount of electrical energy and produces large amount of heat during operation. On the other hand, the backlight of the backlight devices can not be individually adjusted according to a pixel level. Thus the color gamut is limited.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.